Vacuum-tube generator



June 3, 1930. E. Y. ROBINSON 1,760,996

VACUUM TUBE GENERATOR Original Filed June 10 1925 2 Sheets-Sheet l WITNESSES: INVENTOR June; 3, 1930. E. Y. ROBINSON 1,760,996

VACUUM TUBE GENERATOR Original Filed June 10 1925 2 Sheets-Sheet 2 wn' 555329 u INVENTOB 5465/ K/Foh/ISM.

. I BY ATTdRNEY Patented June 3, 1930 UNITED STATES PATENT OFFICE I ERNEST YEOMAN ROBINSON, OF LYMM, ENGLAND, ASSIGNOR TO ASSOCIATED ELEC- TRICAL INDUSTRIES LIMITED, A BRITISH COMPANY VACUUM-TUBE GENERATOR Application filed June 10, 1925, Serial No. 36,139, and in Great Britain June 11, 1924. Renewed February 1, 1930.

This invention relates to vacuum electric tube systems such as oscillation generators, power converters from direct to alternating current and other vacuum tube systems which require the application of various potentials to the grids of the tube devices.

In the case of a three-electrode valve generating retroactively in the ordinary way a sinusoidalvoltage is applied to the grid and negative grid bias of constant value is also applied. lVhen direct current is converted to alternating current by means of three-elec trode valves according to other methods, such for example as that described in the specification of British Letters Patent No. 209.212, the valve is made periodically conducting and non-conducting, by periodically varying the grid bias. For example, in the method according to said Letters Patent, the grid bias may be periodically made negative or positive.

Considering first the case of a valve which is generating oscillations in the ordinary manner the grid bias is provided either by means of a battery or by means of a combination of resistance and capacity whereby the rectified current produced in the grid circuit is caused to charge up the condenser which, by means of the grid leak, is caused to assume a definite negative voltage, so that the appropriate grid bias is obtained. The disadvantages of employing a grid battery are that it is heavy and bulky and, during operation of the valve,it is continuously charged by the rectified grid current, which is undesirable. The disadvantage with the condenser and resistance arrangement (or leaky condenser) is that, should the valve fail to oscillate, the grid bias will not be applied, and it the valve is normally so adjusted that when oscillating the grid bias is highly negative, such as when the valve is a low impedance valve, or as it is when the valve is adjusted for efficient generation and the applied voltage is high, the anode will be over-heated and the valve will soften or even break down. Since such a valve is arranged for producing oscillations in circuits for utilizing them, cases frequently arise in which the valve does not oscillate. 60 For example, in the case of a set destined for use on aeroplanes the antenna might foul a portion of the structure when it is let down, or in other cases the load on the circult might be so great that oscillations are not produced.

It might be said with the capacity-resistance arrangement the grid bias is produced by rectifying oscillations (by means of the grid) which are generated by the valve itself. According tothis invention, a grid bias, either positive or negative as may be required. is produced by rectifying alternating current from a separate source. In the preferred method. the source of these alternating currents, which are rectified to give the grid bias, comprises a vacuum tube converter or oscillator, and the rectifying device comprises a vacuum tube rectifier. For the purposes of obtaining a negative grid bias these two devices may be combined in one vacuum electric tube and circuit.

In carrying out the invention a three-electrode valve is arranged to produce oscillations in an oscillatory anode circuit which is electromagnetically coupled to a coil connected with the grid and the desired grid bias is obtained, according to one arrangement, by a thermionic diode which rectifies alternating current from a suitable source, such as an alternator or a vacuum tube generator, one terminal of which is connected to the anode of the diode and the other terminal of which is connected, through a resistance, to the filament of the diode. A condenser is connected across the resistance and the grid coil of the oscillation valve is connected to one end of the resistance through a choke coil. The cathodes of the oscillation valve and the diode are connected together at their negative ends.

With this arrangement, when alternating electromotive force is supplied, from the alternator or other source, to the diode the anode of the latter assumes a negative potential with respect to its filament, the value of.

which potential is dependent upon the voltage of the source and the resistance connected in series therewith.

In order that the invention may be full understood it will now be described witi reference to the accompanying drawings which are electrical diagrams illustrating the invention, Fig. 1 showing an elementary arrangement thereof, Figs. 2 and 3 showing two arrangements for carrying the invention into practice, while Fig. 4 shows a further arrangement suitable for power conversion.

Referring first to Fig. 1, a three electrode valve 1 is arranged to produce oscillations in an oscillatory circuit 2, being provided with a grid coil 3 coupled with the inductance of the oscillatory circuit 2. The'valve l is provided with the usual source of anode current indicated at 4. The grid bias required for the oscillating valve 1 is obtained by means of a diode 5 which is arranged to rectify alternating current from a suitable source 6 such as an alternator. One terminal of the source 6 is connected to the anode of the diode while the other terminal thereof is connected through a resistance 7 to the cathode of the diode. A condenser 8 is connected across the resistance and the grid coil 3 of the oscillating triode 1 is connected to one end of the resistance through a choke coil 9. The cathodes of the two valves are connected together by means of a conductor 10. A condenser 8a is connected from one end of the grid coil 3 to the conductor 10 as shown.

With the arrangement described, when alternating electromotive force is supplied from the source 6 to the diode 5, rectified current flows in the resistor 7. Consequently, the cathode of the diode 5 will be at a more positive potential than the lower terminal of the source 6. That is, the grid of the triode 1 assumes a negative potential with respect to its cathode the value of which potential is dependent upon the voltage of the source and the magnitude of the resistance In the operation of the system the grid bias is first produced by energizing the cathode of the diode and applying the alternating elect r0 motive force thereto. The high tension supply to the triode is then switched on. The rectified voltage is so chosen that the grid bias .applied to the triode is sufiicient to permit the latter to commence to oscillate and to operate under safe conditions. When the oscillations commence the grid bias is increased byreason of the rectified current produced in the grid circuit'of the triode.

In the system shown in Fig. 2 the oscillating triode 1 is arranged to produce oscillations in an oscillatory circuit 2 comprising, by way of example, an antenna 11 and a loading coil 12 to which are coupled the anode coil 13 of the triode and the grid coil 3 thereof. Power is supplied to the anode of the triode by means, for example, of a direct current generator 4. The grid bias for the triode 1 is provided by means of an auxiliary valve 14 so connected as to produce oscillations in an oscillatory grid circuit 15 to which is coupled an anode coil 16 connected with a high tension source such as a battery 17.

Alternatively, the coil 16 could be connected to the direct current generator 4. The oscillatory circuit 15 is connected, at one end, to the grid of the triode 14 and at the other end through a leaky condenser device comprising the condenser 18 and parallel connected resistance 19, to the cathode.

In the illustrated arrangement the cathodes of the two valves are supplied with alternating current through transformers 20 and 21 the secondary windings of which are connected across the respective cathodes and the primary windings of which are connected in parallel to an alternator 22. The space current, in the ease of both valves, is led to mid point taps of the secondary winding of the filament heating transformers, which taps are connected together by a conductor 23. The leaky condenser 18 is also connected to said mid point taps. The other end of the leaky condenser 18, which is connected to the oscillatory grid circuit 15, is connected through a choke coil 24 to the grid coil 3 of the oscillating valve 1. .A condenser 25 is connected beteween the end of the grid coil 3 which is remote fromthe grid and the mid point tap of the filament heating transformer 20.

IVhen the valve 14 oscillates the grid thereof will assume a negative potential which is applied to the grid of the main valve 1. In operating the system the auxiliary valve 14 is made to generate oscillations, which may be of radio frequency, to provide grid bias for the main valve 1, so that when power is supplied to the anode of the latter it can commence to generate oscillations. Should the valve 1 fail to produce oscillations it will still be operating under safe conditions since grid bias is supplied from the auxiliary valve 14. IVhen the main valve commences to generate oscillations the grid bias will become still more negative owing to the rectified current in the grid circuit. The choke coil 24 prevents undesirable interaction between the valves 1 and 14. i

The circuits of the two valves 1 and 14 may be interconnected in such a manner that should the auxiliary valve fail to operate the anode voltage of the main valve cannot be applied. For this purpose protective relays may be provided in the generator circuit of the auxiliary valve'or the two filaments may be connected in series with one another, or other protective means may be employed.

Referring to Fig. 3 of the drawings the system therein shown is generally similar to that shown in Fig. 2 but includes protective means for the purpose just above mentioned. The direct current generator 4 and the alternating current generator 22 are, for convenience, mechanically coupled together, the generator 22 also supplying the anode current for the auxiliary valve 14 through the step-up transformer 25. Current supply to the cathodes of the two valves and to the transformer 25 is controlled by means of a manually operable switch 26. Since the auxiliary valve 14 is energized from the alternating current generator 22 the grid biasing voltage will vary at the frequency of the generator and such variation may be reduced by employing a condenser 18 of large capacity. The prime mover for the generators 4 and 22 is not shown.

A direct current relay 27 is included in the grid circuit of thegrid-bias generator 14 as shown, this relay controlling, by means of energy derived from a battery or other source 28, the coil 29 of a switch 30 provided in the anode circuit of the main generating valve 1. The coil 29 and switch 30 may constitute an electroma-gnetically operated or contactor switch or the'switch 30 may be of the-manually operable variety provided with a trip coil 29. Control current for the coil 29 may be obtained from the generator 22 instead of from the battery 28. A condenser 31 is connected across the secondary winding of the transformer 25. A key 32 may be provided in the grid circuit of the main valve forthe transmission of telegraphic signals.

In the arrangement described the grid bias generator 14 provides high frequency current modulated at the frequency of the generator 22, which current is partly rectified by means of the grid of the valve, the rectified current passing through the resistance 19 causing a voltage drop therein which is employed for providing grid bias for the main valve 1. The large condenser 18 shunted across the resistance 19 minimizes the variations of the grid biasing voltage.

In the event that the auxiliary valve 14 stops, oscillating grid-current will cease flowing therein. A cessation of grid-current permits the relay 27 to drop out, thus depriving the coil 29 of holding current and ,allow-' ing the switch 30 to open. Upon the opening of the switch 30, the anode-potential supply circuit for the valve 1 is broken, thus protecting the said .tube from damage that would result if it were to be supplied with anodepotential without a sufficiently negative gridbias potential.

Referring to Fig. 4 current from a direct current source 33 is converted by means of two triodes 34 and 35 into single phase alternating current of low frequency such as is used for industrial purposes, the alternating current output terminals being indicated at 36. In the example shown the two triodes 34 and 35 are arranged to pass current alternately, each being rendered alternately wholly conducting and wholly nonconducting in order that the efficiency of generation may be high. .The cathodes of these triodes are heated by means of current from an alternator 37 through a transformer 38. The anodes of the valves 34 and 35 are connected to the terminals of the primary winding of a transformer 39 the secondary winding of which is connected to thealternating current output terminals 36. The positive terminal of the direct current supply 33 is connected to the mid-point of the primary-winding of the transformer.

The grids of the valves 34 and.35 are made alternately positive and negative bymeans of a commutator diagrammatically indicated at 40, so that each valve periodically and alternately passes current with the result that alternating current is produced at the terminals 36. A harmonic suppressing device 41 shown, so that they respectively pass current on alternate half cycles. Thus the terminals 45 and 46' are thereby rendered respectively negative and positive. The cathodesof the diodes 43 and 44 are heated by means of alternating current supplied from the generator 37 through transformers 47 and 48 which have central taps for the space current to the secondary windings thereof in the manner hereinbefore described. Two'condensers 49 and 50 are connected in series with one another between the terminal 45 which is connectedto the anode of the diode 43, and the terminal 46 which is connected to the mid point of the secondary winding of the filament'heating transformer 48. Resistances 51 are preferably shunted across said condensers which should belarge, and the common terminal thereof isconnected to one terminal of the secondary winding of the transformer 42, the other terminal of which is connected to the anode of the diode 44 and to the mid point of the secondary winding of the oathode heating transformer 47. The terminals 45 and 46 are connected as shown to the commutator 40 which reverses ,the polarity of the ing device, said rectifying devicabeing distinct from the vacuum tubes of said vacuumtube osclllator, and automatlc means for 1nterrupting the supply of anode current to the vacuum-tube oscillator upon failure of the grid biasing means.

2. Ina grid-biasing device, a vacuum tube to be biased, a vacuum-tube oscillation generator including a grid, a cathode and a circuit external to the vacuum tube between 1 said grid and said cathode, a connection from a point in said external circuit to the tube to be biased and a current-responsive device in said external circuit controlling the energization of said tube to be biased.

3. In a system comprising a thermionic tube, means for supplying plate-potential to said tube, a relay having normally open contacts included in the plate-potential supply circuit, means including a thermionic device, for deriving grid-biasing potential for said tube, and means whereby said relay is energized when said deriving means becomes operative.

4. In a system comprising a thermionic tube, a source of grid-biasing potential for said tube comprising a thermionic device having a cathode, a source of plate-potential for said thermionic tube, .and means responsive to energizationof said cathode for controlling the application of plate-potential to said thermionic tube from said source.

5. In a system comprising a thermionic tube, a source of grid-biasing potential for v said tube comprising a thermionic device, means for establishing a space current in said thermionic device, means for supplying plate-potential to said thermionic tube, and means whereby plate-potential may be applied to said thermionic tube only during the continuance of space current in said thermionic device. a

6. In a system comprising a thermionic tube, a source of grid-biasing potential for said tube comprising a thermionic device having a cathode, a source of plate-potential for said thermionic tube, a relay device having normally 0 en contacts, means whereby the winding 0 said relay device is energized upon the energization of said cathode, and means whereby the contacts of said relay control the application of plate-potential to said thermionic tube.

7 In a system comprising a thermionic tube, a source of alternating'current comprising a conductive path, means for deriving from said source a grid-biasing potential for said thermionic tube, a source of plate-potential for said tube, and means whereby said tube is deprived of plate-potential when said pat-h becomes non-conductive.

In testimony whereof, I have hereunto subscribed my namethis 19th day of May,

ERNEST YEOMAN ROBINSON. 

